There continues to be a need for enhanced stereo and other sound generating systems for use in a variety of environments including, for example, movie theaters, homes and automobiles. In particular, audience members continue to desire an ever-more intense and realistic entertainment experience. Among the new technologies that have been developed in this regard are sound generating technologies that allow an audience member to hear sounds that appear to be coming from locations outside of the physical environment in which the audience member is situated, e.g., outside a theater. For example, in a movie environment in which an airplane is being displayed on the movie screen, apparently at a location far beyond the physical location of the screen itself, such new technologies can allow an audience member to hear sounds that appear to the audience member as if they had originated from the fictitious, distant airplane rather than from the audio speakers positioned around the theater.
One such technology that has allowed for such simulated sounds to be achieved was developed by F. Richard Moore, and is described in “A general model for spatial processing of sounds”, Computer Music Journal, 7(6):6-15, 1983, which is hereby incorporated by reference herein. To achieve such simulated sounds, this technology models a given physical environment of an audience member as having two nested areas. The outer room is an imaginary acoustic space within which the inner room (or the real performance space, e.g., the theater room) is located. The inner room is denoted by the location of the speakers which simulate the sound heard in the inner room as if the speakers were “openings” connecting the inner and the outer room. The spatial impression is produced by diffusing simulated direct sound rays, early echos, and global reverberation of the sound sources as heard at each speaker location. Based on the location of the source and geometry of the inner and outer rooms, simple ray-tracing algorithms are used to calculate the direct and reflected rays to the speaker locations. Direct paths are simply straight lines to the speaker locations.
FIG. 1 illustrates this Prior Art manner of modeling fictitious sounds coming from a fictitious source positioned outside a region, which allows for the generation of actual sounds by one or more sound sources (e.g., speakers) positioned along the border of the region such that at one or more locations within the region the actual sounds appear as if they were emanating from the fictitious source. More particularly, FIG. 1 shows exemplary paths 8, 10 for first order reflections of sound waves (represented by rays) emanating from a fictitious source 2 located outside of an inner region 4 having a boundary 6, within which could be located audience member(s) (or other listener(s) or listening device(s)), e.g., a room such as a theater chamber, etc.
As shown, the paths 8, 10 are shown to travel from the fictitious source 2 toward an outer boundary 16 of a second, outer region 14 encompassing the inner region 4, at which the paths then are reflected toward the inner region 4. The particular paths shown are those which travel from the fictitious source 2 toward each of four exemplary speaker locations 12 located at corners of the region 4, albeit it will be understood that other paths will also occur and could be shown. The exemplary paths 8, shown as solid lines, are paths that need not traverse the boundary 6 of the inner region 4 in order to arrive at their respective speaker locations 12, while the exemplary paths 10, shown as dashed lines, are paths that need to traverse the boundary 6 and a portion of the inner region 4 in order to arrive at their respective speaker locations.
Other than continuous control over the location of the fictitious source 2, three other parameters are defined to characterize the diffusion pattern of the sound source. Thus, a radiation vector (RV) is defined as follows:RV=(x,y,θ,amp,back),  (1)where x and y denote the location of the source with (0,0) being at the center of the inner room, θ is the source radiation direction, amp is the amplitude of the vector, and back is the relative radiation factor in the opposite direction of θ (0<back<1). Back and θ are used to denote the supercardiod shape for radiation pattern of the sound source. Setting back to zero denotes a strongly directional source and setting back to one denotes an omnidirectional source.
The following equation (2) is used to calculate the amplitude scale factor for a simulated sound ray:
                              r          ⁡                      (            ∅            )                          =                              [                          1              +                                                                    (                                          back                      -                      1                                        )                                    ⁢                                                                                θ                      -                      ∅                                                                                          Π                                      ]                    2                                    (        2        )            where r(ø) is the scale factor and ø is the direction of the ray being simulated. Subsequently, the final attenuation factor for each simulated sound ray is calculated based on the following equations:αi=ρiKiBiDi  (3)
                              D          i                =                  1                      d            i            y                                              (        4        )            where α is the total attenuation factor, ρ is the amplitude scalar determined based on the radiation pattern of the sound source and the angle by which the sound ray leaves the source (see eqn. 2), K is the “cut factor” (zero if a sound ray “cut”s through a wall of the inner room, and one otherwise), B accounts for absorption at reflection points, D is the attenuation factor due to the length of the path calculated based on d, the distance that the ray has to travel, and y denotes the power law governing the relation between subjective loudness and distance.
The delay values for each simulated sound ray is calculated by the relation
                              τ          i                =                              R            ×                          d              i                                c                                    (        5        )            where τ is the delay value, R is the sampling rate in Hz, di is the distance between the source and a speaker, and c is the speed of sound. Moore made a partial, though fairly complete, practical and useful, implementation of the general model in the “space unit generator” of cmusic. This implementation used a fixed 50 millisecond fade time for turning sound rays on and off based on the result of the “cut” factor of each ray and the inner walls.
The above-described scheme of Moore works well so long as a given fictitious source such as the source 2 can be assumed to be located outside of the boundary 6 on which the speakers are located, at a considerable distance from that boundary 6. The scheme simulates spatial impressions by assuming that the sounds of an outer room are heard inside an inner room, such that the model's results are more convincing when the source is outside the inner room. In most applications it is not desired for the inner room to have a physical presence; meaning that when a sound source passes through a wall, it is usually not meant to be heard as such.
However, the above-described scheme does not address the need for allowing simulated sounds of things (both animate and inanimate) located within the boundary 6 along which speakers are located (e.g., within the inner region 4). When the source is inside the inner region, the model can no longer be applied realistically, hence the undesirable effect of speakers in opposite sides turning on and off abruptly when a sound source passes through an inner wall. For example, if a source comes close to a wall of the inner region or if it passes through the boundary of that region, turning on and turning off speakers with a fixed 50 millisecond delay in opposite speakers to the wall would be perceived as noticeable distraction.
For at least these reasons, therefore, it would be advantageous if an improved method and system could be developed that allowed for sounds to be generated within a region such as (but not limited to) a theater, where the generated sounds gave the appearance to audience member(s) (or other listener(s) or listening device(s)) within the region that the sounds were emanating from one or more thing(s) located within the region instead of outside of the region (or in addition to).